1. Field of the Invention
This invention relates to an analytical system for evaluating test elements having means of determining whether a sufficient amount of sample liquid was evenly applied to a test element application zone. To this end, a first embodiment of the invention comprises of a control unit for activating at least two sources of light independently from each other, wherein said light sources illuminate separate or at least not fully overlapping areas of the application zone of the evaluation zone of the test element. Light reflected by the evaluation zone or transmitted by the evaluation zone is detected by at least one sensor which generates an output signal proportional to the intensity of light. An evaluation unit receives a first output signal when the first of the light sources of which there are at least two is activated and receives a second output signal when the second of the at least two light sources is activated. The output signals are converted by the evaluation unit into measured values and the measured values are compared with each other. When the deviation of the first measured value from the second measured value is sufficiently small, a sufficient amount of sample liquid has been applied to the test element. If the deviation exceeds a preset threshold value, then the amount of sample was either too small and/or was incorrectly applied and the analytical system gives an error warning.
2. Description of the Related Art
In the prior art the problem of test elements generating erroneous results when either too little sample liquid is applied to a test element or when the sample liquid is incorrectly, i.e. not fully applied to predetermined sites has been known for a long time. In the past the user himself has to visually monitor whether the sample liquid was applied to the correct site in sufficient quantity. Visual monitoring by the user is however of poor reliability, particularly for test elements for determining blood glucose levels as used by diabetics whose sight is often impaired by the disease. To solve the said problem, an apparatus is described in the European Patent EP-B-0 087 466, which estimates on the basis of the absorption of water in the infrared region of the electromagnetic spectrum whether the amount of sample is sufficient. The suggested apparatus is however disadvantageous for a portable system such as for example for the measurement of glucose in blood because in addition to the means required for quantitative evaluation, an infrared transmitter and receiver are necessary. Furthermore, the apparatus described in EP-B-0 087 466 performs an integral examination to determine whether a sufficient amount of sample liquid has been applied. For the performance of analytical tests using test elements however not only the total amount of test liquid is of importance but rather also the distribution of sample liquid over the sample application zone. Using this apparatus such cases can not be easily identified in which sufficient sample liquid has been applied but has been unfavorably positioned such that the reagent area of the test element is unevenly or incompletely wetted with sample liquid.